In industrial plants such as refineries and chemical plants, there are large amounts of fluids flowing through process pipelines. In order to run these plants effectively, it is necessary to know the composition of these fluids. Despite advances in automatic sampling/analysis systems, the prevalent method is to remove a fluid sample and perform lab analysis to determine its composition.
Conventionally, the pipeline is tapped and the fluid is regulated by a throttling valve and poured into a sample bottle. The conventional method is adequate if the fluid pressure is constant and low (less than 15 psig), the fluid is noncorrosive, or the throttling valve performs perfectly. Unfortunately, in refineries and chemical plants the fluid streams are frequently of higher pressures, and the fluids are highly corrosive. These same fluids tend to corrode, erode, or plug the throttling valves, rendering them ineffective. Specialty valves are frequently unavailable, expensive, or unreliable due to their complexity. If the fluid to be sampled is hazardous or produces toxic fumes, the sampling system is usually surrounded by an enclosure to protect the operator from being splashed by the fluid. Despite such precautions, many operators are injured each year when drawing a sample of hazardous fluids (such as acid) because no safe and effective sampling system is readily available.
If the process line is under vacuum rather than positive pressure, the conventional method involves attaching an eductor to draw the fluid. Alternate methods include temporarily shutting down the vacuum source. It is often unfeasible to shut down the vacuum source, and use of an eductor can contaminate the sample or add expense depending on the cost of the driving fluid. It is desirable to have a single sampling system that can obtain samples from a pipeline which is either under vacuum or positive pressure.